With the continuous expansion of the data center market of the global Internet, the amount of the electric power supplied to the data center is gradually increased, and the power supply demands on the processor of the data center are gradually increased. Therefore, a converter system with a two-stage configuration is usually required to power the processor of the data center. The two-stage converter system includes a front-stage converter and a rear-stage converter. The front-stage converter needs higher efficiency. For example, the front-stage converter is a LLC converter, a phase-shifted full-bridge converter or a switched tank converter. In addition, the rear-stage converter is usually a buck converter. Since the two-stage converter system has high frequency, small volume, high dynamic response and associated benefits, the two-stage converter system is widely applied to the data center.
In comparison with the LLC converter and the phase-shifted full-bridge converter, the switched tank converter is not equipped with a transformer. Consequently, the volume of the switched tank converter is smaller than the volume of the LLC converter and the volume of the phase-shifted full-bridge converter. Moreover, at the low transformer ratio, the operating efficiency of the switched tank converter is higher than the operating efficiency of the LLC converter and the operating efficiency of the phase-shifted full-bridge converter. Recently, the switched tank converter is widely used as the front-stage converter of the two-stage converter system.
The conventional switched tank converter includes a plurality of conversion units. In other words, the switched tank converter has a multi-stage conversion structure. According to the transformer ratio, the conventional switched tank converters are divided into two types, i.e., a first-type switched tank converter and a second-type switched tank converter. As the stage number (or the conversion unit number) of the first-type switched tank converter is increased by one, the transformer ratio is added by 1. That is, if the first-type switched tank converter has an N-stage conversion structure, the highest transformer ratio is (N+1). As the stage number (or the conversion unit number) of the second-type switched tank converter is increased by one, the transformer ratio is added by 2. That is, if the second-type switched tank converter has an N-stage conversion structure, the highest transformer ratio is 2N.
However, in case that the high transformer ratio is required, the applications of the first-type switched tank converter and the second-type switched tank converter are limited. For example, the first-type switched tank converter needs a 15-stage conversion structure to achieve the transformer ratio of 16:1, and the second-type switched tank converter needs an 8-stage conversion structure to achieve the transformer ratio of 16:1. That is, the circuitry of the first-type switched tank converter or the second-type switched tank converter is complicated and not cost-effective.
Therefore, there is a need of providing an improved switched tank converter.